HIMEM.SYS--Notes

HIMEM tests the reliability of your extended memory

The MS-DOS 6.22 version of HIMEM.SYS includes a special safety feature: it
tests your computer's extended memory each time your computer starts. HIMEM
tests the memory by writing and reading data to each memory address and
checking for differences in the data. If the data HIMEM reads from an
address differs from the data it just wrote to that address, then the memory
at that address is unreliable. Unreliable memory can cause system
instability or loss of data. HIMEM's memory test is more thorough than the
standard power-up memory test performed by most computers.

If HIMEM detects unreliable memory, it displays the following message and
does not load:

    ERROR: HIMEM.SYS has detected unreliable extended memory at address
    XXXXXXXXh.

If you receive this message, you should have your computer's memory checked
by a qualified computer hardware technician. Although you can disable the
memory test and load HIMEM by using the /TESTMEM:OFF switch, it's not
advisable to do so until you have had the memory checked by a technician.

Default memory allocation

Only one program at a time can use the high memory area (HMA). If you omit
the /HMAMIN=m switch (or set it to 0), HIMEM reserves the HMA for the first
program that requests it and that meets the memory requirements set by the
/HMAMIN=m switch. To ensure the most efficient use of your system's high
memory area, set /HMAMIN=m to the amount of memory required by the program
that uses the most HMA memory.

Loading MS-DOS into the high memory area

HIMEM or another XMS driver must be loaded in order to load MS-DOS into the
high memory area (HMA). You load MS-DOS into the HMA by using the DOS=HIGH
command in your CONFIG.SYS file. (The DOS=HIGH command can appear anywhere
in the CONFIG.SYS file.)